148 MORPHOLOGY AND EVOLUTION
each jaw is reduced in size, the crowns are much wrinkled, and the cusps are small. The fifth cusp on the last molar tooth in the lower jaw is variable. The last molar tooth is really degenerating, so it cannot be used for taxonomic purposes.
Taking the dentition as a whole the Chimpanzee approaches Man more closely than does any other Ape.
Accessory teeth are less frequent in the Chimpanzee than in the G-orilla and Orang, and Duckworth (50) points out that this applies to both precanine and post-canine teeth. Bat no case of double-rooted canine teeth has been recorded in any of the Apes.
The actual order in which the permanent teeth erupt has not yet been established, but Keith (100) points out that the canine teeth usually erupt before the last molar teeth. The first permanent molar tooth is the first permanent tooth to appear. The permanent dentition is completed between the eleventh and thirteenth years, giving it as the eleventh or twelfth year, and Keith (100) as the twelfth or thirteenth year.
DENTITION IN THE G-OEILLA.
The upper central incisors are larger than the upper lateral incisors, but the disproportion is not so great as in the Orang and Chimpanzee. The crowns are large. The canines form large tusks which serve as formidable weapons. The diastemataare as in the other Apes.
The upper premolar teeth differ from those in the Chimpanzee in being equal in size; in the Chimpanzee the first is larger than the second. Each has three roots and two cusps, of which the outer is the larger; sometimes two minute cusps are present behind the